Internal combustion engines rotate at a speed that varies almost sinusoidally about a nominal speed. This variation is associated with combustion occurring successively in the cylinders. This phenomenon is typical of internal combustion engines, it is referred to as “engine acyclism”, and it is particularly significant when the compression ratio is high (diesel engine) and the number of cylinders is small. This acyclism in the engine speed is transmitted to accessories such as a water pump, power-assisted steering, air conditioning, an alternator, etc. . . . .
Some of these accessories, such as an alternator, possess high levels of inertia. Such inertia coupled with acyclism generates high dynamic torque levels. These torque levels are transformed into very great tension differences in a belt.
When a belt passes through tension levels that are too low, there may be sufficient instantaneous slip for the belt to slide, cease to drive, and be noisy.
When the belt possesses a coefficient of friction that is too high, a phenomenon can be observed that generates a significant level of noise by the belt sticking and then suddenly slipping (stick-slip noise).
A third phenomenon giving rise to noise is relative misalignment between two successive pulleys. This phenomenon is highly dependent on factors such as:                strand length;        nature of the materials (moduluses of the rubbers);        dimensions of the belt (thicknesses of its various layers); and        the coefficient of friction between the pulley and the blanks of the teeth of the belt.        
The higher the coefficient of friction, the greater the level of noise.
The purpose of covering the teeth with a non-woven fabric is to reduce the coefficient of friction.
Known solutions consist in placing a non-woven fabric directly on a non-vulcanized blank, and then in forming a belt by vulcanization. Patents U.S. Pat. No. 4,747,812, U.S. Pat. No. 4,892,510, and EP 0 774 594 propose belts having teeth that are covered in a non-woven fabric that is molded and vulcanized thereon. By way of example, the non-woven fabric may be based on pulp and rayon.
U.S. Pat. No. 6,793,599 proposes a cellulose non-woven fabric molded on a fiber-loaded rubber constituting the teeth of the belt. U.S. Pat. No. 6,824,485 proposes infusing an elastomer compound in a non-woven fabric, the compound being the same as that constituting the teeth.
US patent application No. 2004/214675 proposes a belt having teeth covered in a woven or non-woven fabric, itself covered in a film of elastomer or plastomer having high ethylene content.
The methods described in the above-mentioned patents have the drawback that, during molding, the raw material of the tooth rubber passes through the non-woven fabric. The tooth rubber is therefore to be found on the surface, level with the fibers of the non-woven fabric where it can generate noise phenomena.
It is known that belts having tooth rubber based on ethylene alpha olefin (ethylene propylene terpolymer rubber (EPDM) or ethylene propylene rubber (EPM)) generate noise in particular on cold starting, when idling, or indeed when low temperatures are low in winter.